In recent years, wireless electric power transmitting systems that wirelessly supply electric power to portable devices, such as a smartphone and a laptop personal computer, have been put to practical use. Such wireless electric power transmitting systems include, for example, those described in Patent Document 1 and Patent Document 2.
Patent Document 1 discloses an electromagnetic induction type wireless electric power transmitting system. The electromagnetic induction type wireless electric power transmitting system includes an electric power transmitting apparatus and an electric power receiving apparatus. The electric power transmitting apparatus includes an electric power transmitting coil, and the electric power receiving apparatus includes an electric power receiving coil. Electric power is thus transmitted between these coils through electromagnetic induction.
Patent Document 2 discloses an electric field coupling type wireless electric power transmitting system. The electric field coupling type wireless electric power transmitting system includes an electric power transmitting apparatus and an electric power receiving apparatus. The electric power transmitting apparatus includes an electric power transmitting electrode, and the electric power receiving apparatus includes an electric power receiving electrode. Electric power is thus transmitted between these electrodes through electrostatic induction.
FIG. 11 is an equivalent circuit diagram of the electric field coupling type wireless electric power transmitting system disclosed in Patent Document 2. This electric field coupling type wireless electric power transmitting system includes an electric power transmitting apparatus 1101 and an electric power receiving apparatus 1201, and electric power is transmitted through coupling capacitance Cm between capacitance C1 of the electric power transmitting apparatus 1101 and capacitance C2 of the electric power receiving apparatus 1201. The electric power transmitting apparatus 1101 includes an LC resonant circuit formed by an inductor L1 and the capacitance C1, and the electric power receiving apparatus 1201 includes an LC resonant circuit formed by an inductor L2 and the capacitance C2. In this wireless electric power transmitting system, two resonant frequencies are generated when the electric power transmitting apparatus 1101 and the electric power receiving apparatus 1201 are coupled so as to couple the two resonant circuits. An operating frequency (electric power transmitting frequency) of a voltage generator 11 of the electric power transmitting system is set to a frequency that is intermediate between these resonant frequencies.    Patent Document 1: Japanese Unexamined Patent Application Publication No. 2009-118587    Patent Document 2: International Publication No. WO2011/148803
With the electric field coupling type wireless electric power transmitting system as disclosed in Patent Document 2, the electric power receiving apparatus may be damaged if the electric power receiving apparatus is removed from the electric power transmitting apparatus while the electric power receiving apparatus is placed on the electric power transmitting apparatus so as to transmit electric power.